1. Field of the Invention
The invention relates to the catalytic copolymerization of ethylene with high activity Mg and Ti containing complex catalysts in a low pressure gas phase process to produce polymers having a density of about 0.91 to 0.94 and a melt flow ratio of about .gtoreq.26 to .ltoreq.40.
2. Description of the Prior Art
To be commercially useful in a gas phase process, such as the fluid bed processes of U.S. Pat. Nos. 3,709,853; 4,003,712 and 4,011,382; Canadian Pat. No. 991,798 and Belgian Pat. No. 839,380, the catalyst employed must be a high activity catalyst, that is, it must have a level of productivity of .gtoreq.50,000 and preferably, .gtoreq.100,000 pounds of polymer per pound of primary metal in the catalyst. This is so because such gas phase processes usually do not employ any catalyst residue removing procedures. Thus, the catalyst residue in the polymer must be so small that it can be left in the polymer without causing any undue problems to either the resin manufacturer, or to a party fabricating articles from the resin, or to an ultimate user of such fabricated articles. Where a high activity catalyst is successfully used in such fluid bed processes, the heavy metal content of the resin is of the order of .ltoreq.20 parts per million (ppm) of primary metal at a productivity level of .gtoreq.50,000. Low catalyst residue contents are also important where the catalyst is made with chlorine containing materials such as the titanium, magnesium and/or aluminum chlorides used in some so-called Ziegler or Ziegler-Natta type catalysts. High residual chlorine values in a molding resin will cause pitting and corrosion on the metal surfaces of the molding devices. Molding resins having Cl residues of the order of .gtoreq.200 ppm are not commercially useful.
British Pat. No. 1,310,547, published in March 1973, describes the preparation of high density (&gt;0.96 g/cc) ethylene homopolymers or copolymers with a supported catalyst. This catalyst is a reaction product of a product prepared by grinding together (preferably in a ball mill) either (i) a magnesium halide and a titanium addition compound, or (ii) a polyvalent titanium compound, an electron donor compound and an organometallic compound or hydride of a Group I to III metal, such as aluminum. The examples of this patent describe the preparation of the homopolymers and copolymers in a slurry process.
U.S. Pat. No. 3,888,835, which issued in June 1975, describes the homopolymerization or copolymerization of ethylene in a slurry process at high temperatures in the presence of a catalyst consisting of (A) a co-comminuted (ball-milled) composition of a titanium halide, an aluminum halide-ether complex and a magnesium halide, and (B) an organoaluminum compound. The polymerization activity of this catalyst is described as very high. Another advantage described in this patent, of using such catalyst, is that the aluminum halide-ether complex used in the catalyst preparation is soluble in hydrocarbon solvents and is removed from the polymer product by filtration.
U.S. Pat. No. 3,991,260, which issued in November 1976, describes the homopolymerization or copolymerization of ethylene in the presence of a catalyst prepared by copulverizing (in a ball mill) a magnesium dihalide, particular aluminum compounds, and vanadium or titanium compounds such as titanium dichloride or titanium trichloride, and wherein the Mg/Al molar ratio in the catalyst ranges from 1:0.01 to 1:1. The polymerization reaction is conducted in a slurry process at high temperatures. The catalyst is described as having high activity.
Thus, these patents which disclose the use of particular ball-milled Mg--Ti containing catalysts, disclose the use of such catalysts, primarily, in a slurry process and not a gas phase process operating under a pressure of &lt;1000 psi.
U.S. patent application Ser. No. 892,325, filed Mar. 21, 1978, and refiled as Ser. No. 014,414 on Feb. 27, 1979 in the names of F. J. Karol et al., and entitled Preparation of Ethylene Copolymers In Fluid Bed Reactor, and assigned to the same assignee as is the present patent application, discloses that ethylene copolymers, having a density of 0.91 to 0.96, a melt flow ratio of .gtoreq.22 to .ltoreq.32, and a relatively low residual catalyst content can be produced in granular form, at relatively high productivities if ethylene is copolymerized with one or more C.sub.3 to C.sub.8 alpha olefins in a gas phase process with a specific high activity Mg--Ti containing complex catalyst which is blended with an inert carrier material.
U.S. patent application Ser. No. 892,322, filed Mar. 21, 1978, and refiled as Ser. No. 012,720 on Feb. 16, 1979 in the names of G. L. Goeke et al, and entitled Impregnated Polymerization Catalyst, Process For Preparing, and Use For Ethylene Polymerization, and assigned to the same assignee as is the present patent application, discloses that ethylene copolymers having a density range of 0.91 to 0.94, a relatively low residual catalyst content and a relatively high bulk density can be produced at relatively high productivities in a gas phase process if the ethylene is copolymerized with one or more C.sub.3 to C.sub.8 alpha olefins in the presence of a high activity Mg--Ti containing complex catalyst impregnated in a porous inert carrier material.
The above noted U.S. patent applications Ser. Nos. 892,325; 892,322; 014,414 and 012,720 are hereinafter referred to as The Prior U.S. Applications.
However, the catalyst preparation procedures disclosed in The Prior U.S. Applications are relatively complex and the precursor compositions of Mg, Ti and an electron donor are formed in such procedures by crystallization or by precipitation of the precursor compositions. Additionally, the manner of activating the catalysts of The Prior U.S. Applications is critical in order to obtain an active material. This activation process is conducted by one of two procedures. In the first procedure, the precursor composition is completely activated outside of the reactor. In the second activation procedure, the precursor composition is partially activated outside the reactor and the partially activated precursor composition is fed to the polymerization reactor where the activation is completed with additional activator compound. Further, the polymers produced with the catalysts of The Prior U.S. Applications have a relatively narrow molecular weight distribution, Mw/Mn, value of about 2.7 to 3.8. Additionally, the catalysts of The Prior U.S. Applications require the use of a relatively high comonomer concentration in the reactor in order to produce the copolymers described therein. This results in higher production costs for the ethylene copolymers.